Variable electric resistance semiconductor devices



Jan. 6, 1959 J. M. B. JARRET ET AL 2,867,043

VARIABLE ELECTRIC RESISTANCE SEMI-CONDUCTOR DEVICES Filed 001:. 2, 1953United States Patent VARIABLE ELECTRIC RESISTANCE SEMI- CONDUCTORDEVICES Jean Marie Baptiste Jarret and Jacques Henri Jarret,

Lyon, France, assignors to Les Applications Electroniques desCaoutchoucs (A. E. C.), Courbevoie, France, a corporation of France Thepresent invention relates to variable electric resistance semi-conductordevices of the kind described in our U. S. patent'application Ser. No.136,932, filed January 5, l950,.now Patent No. 2,690,489, issuedSeptember 28, 1954, for ConductorDevices Having a Variable ElectricResistance. Such'devices include semi-conductor elements made of amaterial having a rubber-like elasticity (rubber or another equivalentplastic material, and in particular silicone) in which are incorporatedvery fine conductor particles (carbon) having for instance an averagediameter lower than five hundredths of a micron.

The chief object of the present invention is to provide devices of thiskind which are better adapted to meet the requirements of practice thanthose known up to the present time and in particular which are morestable.

The chief feature ofour invention consists in combining with suchdevices means for exerting an alternating mechanical stress between thesemi-conductor element and the electrode with which it cooperates,whereby a vibratory effect takes place.

A preferred embodiment of the present invention will be hereinafterdescribed with reference to the accompanying drawings, given'merely byway of example, and in which:

The only figure is a diagrammatical sectional view of a variable contactresistor device for measuring displacements, made according to ourinvention.

The apparatus shown by the drawing is intended to indicate smalldisplacements of an element by means of the variations of resistanceproduced in the semi-con.- ductor in response to such displacements.

Our experiment in this field shows that when we place in contact witheach other under a given electrical voltage a metallic electrode and asemi-conductor element carried by a rigid support, the contactresistance does not immediately assume a stable value. After the partshave been placed in contact with each other, and even if the respectivepositions of the metallic electrode and of the semi-conductor supportare perfectly fixed, the contact resistance in the circuit including theelectrode and the semi-conductor element keeps varying to a substantialdegree, and it may in particular drop from to 50%, according to theexperimental conditions, during a time which is variable and may rangefrom some minutes to some hours and even to some days.

This involves considerable difficulties in the use of such devices formeasuring or detecting aperiodic or low frequency mechanical phenomenonswhich act upon the contact of the semi-conductor with the metallicelectrode.

According to our invention, we subject the contacting parts tovibrations which quickly or instantaneously stabilize the electricalcontact resistance or the mean value of this resistance.

For instance, these vibrations (that is to say this reciprocatingmovement) are imparted to the metallic electrode and the semi-conductorelement is carried by a fixed support (or at least a support which ismovable only in response to the displacements to be measured or toanother phenomenon to be recorded). Of course, we might use the reversearrangement, that is to say keep the metallic electrode fixed and impartthe vibratory displacements to the semi-conductor element.

Preferably, the reciprocating movement to be applied will be in the samedirection as the displacement to be measured (when the apparatus isintended for such a measurement), and its frequency will besubstantially higher than that of the phenomenon to be detected. Theamplitude of the reciprocating movement thus applied will beadvantageously chosen higher than that of the phenomenon to be detected,and in particular to the range of amplitudes for the measurement to bemade.

In the construction shown by the drawing, the apparatus includes:

An electrode I intended to cooperate with the pellet which constitutesthe semi-conductor element, this electrode being carried by an elasticsupport 2 subjected to the action of an electro-magnet 3 the coil 4 ofwhich is fed with currents of the desired frequency (for instanceperiods per second) from an alternating current source 17 connectedthrough conductors 15 and 16 with said coil 4. Said support mayconstitute the armature of the magnetic circuit;

A pellet 5 made of a semi-conductor material, this pellet being intendedto give with the electrode 1 a variable contact resistance and beingcarried by a support 6, preferably insulated at 7;

And means for transmitting relative displacements to said support 6 andits pellet 7-in response to the displacements, lengths or phenomenons tobe measured. Such means are constituted, in the embodiment illustratedby the drawing, by a mechanical contact member 8 connected to support 6and provided with means for guiding or positioning said member such asdiaphragms 9.

The whole is mounted in a casing 10.

The apparatus further comprises an electrical circuit including a sourceof current 11 and a measurement apparatus 12, this circuit beingconnected at 13 and 14 to the contact resistance formed by thesemi-conductor element and the metallic electrode.

The apparatus is adjusted so that when coil 4 is not energized, there isno contact between electrode 1 and pellet 5. As soon as the alternatingenergizing is applied, the electrode vibrates and periodically comesinto contact with pellet 5. This produces an alternating contactresistance which corresponds to a given position of the pointer ofammeter (or other like apparatus) 12 on the dial of this apparatus. Thisposition, which corresponds to the average value of the contactresistance, will be for instance on graduation zero (any adjustmentmeans may be provided in order to obtain this position of adjustment,said means acting through abutments or other means upon one of thefactors of the system, for instance upon the relative positions of restof electrode 1 and pellet 5).

As soon as mechanical member 8 is actuated for a measurement operation,a variation of pressure is obtained whichis instantaneously translatedby a deflection of the pointer of ammeter 12.

Such an apparatus makes it possible for instance to measure with aprecision of about 0.2 micron variations of length averaging 20 microns.

Our invention makes it possible to provide high accuracy apparatus suchas comparators, extensometers, balances, pressure gauges, and so on, andin a general manner all apparatus making use of contact resistors of theabove mentioned kind, especially in the case of aperiodic or lowfrequency phenomenons.

In a general manner, while We have, in the above de-- scription,disclosed what we deem to be practical and efi'icient embodiments of ourinvention, it should be well understood that We do not wish to belimited thereto as there might be changes made in the arrangement,disposition and form of the parts without departing from the principleof the present "invention as comprehended within the scope of theaccompanying claims.

' What we claim is:

1. A measurement apparatus of the type described which comprises, incombination, an electric circuit including in series a source ofcurrent, a semi-conductor element made of a material having arubber-like elasticity in which are incorporated very fine conductorparticles, an electrode arranged to cooperate with said element, and anelectric measurement device in said circuit responsive to resistancevariations therein, means for imparting a vibratory auxiliary relativedisplacement to said semi-conductor element and said electrode to bringthem periodically into and out of contact with each other, and'means forimparting to said two last mentioned parts, in a direction parallel tosaid vibratory displacement, a "main relative displacement to bemeasured, the amplitude of said vibratory'auxiliary displacement beinghigher than the range of said main relative displacement.

2. A measurement apparatus of the type described which compris'esQincombination, an electric circuit including in series a source ofcurrent, a semi-conductor element made of a material having arubber-like elasticity'in' which are incorporated very fine conductorparticles, an electrode arranged to cooperate with said element, and anelectric measurement device in said circuit responsive to resistancevariations therein, means for resiliently holding said semi-conductorelement and said electrode at a small distance from each other, meansfor imparting a vibratory auxiliary relative displacement to said lasttwo mentioned parts to bring them periodically into and out of contactwith each other, and means for imparting to said two last mentionedparts, in a direction parallel to said vibratory displacement, a mainrelative displacement to be measured.

3. A measurement apparatus of the type described which comprises, incombination, an electric circuit including in series a source ofcurrent, a semi-conductor element made of a material having arubber-like elasticity in which are incorporated very fine conductorparticles, an electrode arranged to cooperate with said element, and anelectric measurement device in said circuit responsive to resistancevariations therein, a casing containing said semi-conductor element,resilient means for holding said semi-conductor element in said casing,means for elastically suspending said electrode in said casing at asmall distance from said semi-conductor element, said electrode being,in the state of rest, out of contact with said semi-conductor element,an electro-magnet inserted in said circuit for imparting a vibratoryauxiliary relative displacement to said electrode with respect to saidcasing to bring said electrode periodically into and out of contact withsaid semi-conductor element, and means for transmitting to saidsemi-conductor element, in a direction parallel to said vibratorydisplacement, a main relative displacement to be measured.

References Cited in the file of this patent UNITED STATES PATENTSSkrobish May 3, 1955

